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    SubjectRe: [PATCH v4 10/10] x86-64: Add CONFIG_UNSAFE_VSYSCALLS to feature-removal-schedule
    On Tue, May 31, 2011 at 2:34 PM, Andi Kleen <andi@firstfloor.org> wrote:
    >> +What:        CONFIG_UNSAFE_VSYSCALLS (x86_64)
    >> +When:        When glibc 2.14 or newer is ubitquitous.  Perhaps mid-2012.
    >> +Why: Having user-executable code at a fixed address is a security problem.
    >> +     Turning off CONFIG_UNSAFE_VSYSCALLS mostly removes the risk but will
    >> +     make the time() function slower on glibc versions 2.13 and below.
    >
    > I disagree with this description (and the whole idea really)
    >
    > First it's time+gettimeofday+vgetcu, not just time.
    >
    > A more accurate description is
    >
    > "will make all x86-64 Linux programs written to the original pre
    > vDSO syscall ABI significantly slower"

    Well, if this series goes in, then gettimeofday and getcpu are already
    slower. It's just time that would get even slower later on.

    >
    > And the assumption that all world is using glibc is still as bad
    > as it was on the first po.st

    As opposed to?

    uclibc and klibc don't appear to use vsyscalls or the vdso.

    dietlibc is hardcoded to use the vsyscall. Are there any
    performance-critical programs using dietlibc?

    I don't think that Bionic runs on any released x86-64 systems.

    >
    > And it's still a bad idea. Especially since there's a much better
    > alternative anyways for the "security problem" which has none of
    > these drawbacks.

    What's the alternative?

    --Andy
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